VEGETATIVE FILTER STRIP BUFFERS
A paper to be submitted to Journal of Soil and Water ConservationD.F. Webber, S.K. Mickelson, T.L. Richard, and H.K. Ahn
Abstract
This study quantifies the effects of windrow composting practices and vegetative filter strip (VFS) buffers on losses of runoff (RO), runoff percent of rainfall (RO%), total solids (TS), nitrate-nitrogen (NO3-N), ortho-phosphorus (PO4-P), and total-phosphorus
(TP) during natural rainfall events. Runoff data from six events were collected during June-July (early season) and August-September (late season) 60-day composting periods from 2002-2004 at an Iowa State University research farm near Ames, central Iowa, USA. Runoff treatments were comprised of three compost windrow:VFS buffer area ratios that included 1:1, 1:0.5, and 1:0 (no buffer) control. The 1:1 and 1:0.5 area ratios represented a 6 m x 23 m (20 ft x 75 ft) fly ash composting pad area compared to VFS buffer areas of equal and one-half size, respectively. All treatments had three replications for a total of nine runoff plots distributed in a randomized complete block design. Results from the study indicate significantly higher levels (p < 0.05) of RO, RO%, TS, NO3-N, PO4-P, and TP from the 1:0 control plots compared to the 1:1 and 1:0.5 plots.
Results also show the 1:1 and 1:0.5 VFS buffer treatments were not significantly different (p < 0.05). Average runoff loss reductions from the 1:1 and 1:0.5 plots were 98 and 93 percent, respectively, compared to the 1:0 control plots. These results reflect the effectiveness of VFS buffers for reducing runoff and contaminant losses from a windrow composting site. Compost nutrient mass balance analysis results indicate 26-41 percent of PO4-P was lost from the compost windrows during the 2004 composting periods.
However, only 0.1-0.4 percent of PO4-P was lost to runoff from the 1:0 control plots. We
hypothesize the significantly lower PO4-P losses in runoff may be attributed to potential
Introduction
The management and utilization of livestock manures continue to pose hazards to the quality of receiving streams and lakes. In the US, two-thirds of the total beef cattle feeding is practiced in the central and southern Great Plains (Krause, 1991). Handling of manure produced in large feedlots and dairies is a significant environmental problem for water, air, and land pollution. Manure is an excellent source of organic matter and plant nutrients, but even under proper management, conventional manure utilization can have negative impacts. Land application of manure to agricultural fields can elevate runoff concentrations of nutrients such as nitrogen (N), carbon (C), and phosphorus (P) (Westerman et al., 1987; Edwards and Daniel, 1993; Heathwaite et al., 1998). Surface runoff of nutrients from agricultural fields is a major source of water pollution in surface waters in the US (Parry, 1998). One strategy to minimize the adverse effects of livestock manure on the environment is windrow composting.
Windrow composting consists of placing manure and other raw materials in long narrow piles or windrows which are agitated or turned on a regular basis (Rynk et al., 1992). Studies have shown that composted manure is less hazardous to the environment (Eghball and Power, 1999; Vervoort et al., 1998) and much of the mineral N is converted to more stable organic forms (Rynk et al., 1992). Compost also has been shown to significantly reduce P in runoff from road construction sites (Jurries 2003) and nitrate (NO3-N) leaching relative to conventional fertilizers (Maynard, 1993). However, one of
the disadvantages of composting is nutrient loss during the composting process, which can occur through leaching, runoff, and volatilization (Christensen, 1983, 1984; Richard and Chadsey, 1994; Eghball et al., 1997; Tiquia et al., 2000). Mass balance analysis results of a composting site indicated 20-60 percent losses of N, P, and potassium (K) during composting processes (Tiquia et al., 2002), of which the most significant losses were runoff and leachate (Garrison et al., 2001). Seymour and Bourdon (2003) reported concentrations of NO3-N, ortho-P (PO4-P), and K were highest in leachate compared to
runoff samples from compost windrows under natural rainfall conditions. Wilson et al. (2004) reported that approximately 68 percent of rainfall incident on saturated compost windrows from both natural and simulated rainfall events resulted in runoff.
Vegetative filter strip (VFS) buffers are bands of vegetation located downslope of cropland or other potential pollutant source areas. These buffer strips provide erosion control and filter nutrients, pesticides, sediment, and other pollutants from agricultural runoff by reducing the sediment carrier and through interception-adsorption, infiltration, and degradation of pollutants dissolved in water (Dillaha et al., 1989). VFS buffers also have been suggested as a best management practice (BMP) that has been shown to reduce sediment and nutrient losses in a range of agricultural settings, including crop fields and feedlots (Magette et al., 1989; Patty et al., 1997). The effectiveness of VFS buffers in controlling pollutants from cropland also has been assessed by several researchers (Dillaha et al., 1985; Mickelson and Baker, 1993; Lee, 2000). These researchers found that VFS buffers have potential for significantly improving the water quality of runoff. However, the effectiveness of VFS buffers depends on many factors, such as vegetation species, soil type, soil texture, type of contaminant, slope of the runoff area, activities on the runoff area (i.e. tillage), and field condition (Dillaha et al., 1989; Arora et al., 1996; Schmitt et al., 1999; Lee, 2000; Abu-Zreig et al., 2003; Goel et al., 2004; Petersen and Vondracek, 2006).
Proper windrow composting site selection is critical to many aspects of a composting operation, including materials transport, road access, and neighborhood relations. From an environmental management perspective, critical issues are soil type, slope, and the nature of the buffer between the site and surface or groundwater resources (Richard, 1996). Since NO3-N and other nutrients move through the soil and into streams
as subsurface flow, or leach down to the groundwater (Tiquia et al., 2002; Garrison et al., 2001), soil permeability is an important factor that impacts windrow composting site design. Consequently, for some windrow composting facilities, a working surface of gravel, compacted sand, oiled stone, or even asphalt or concrete may be appropriate (Richard, 1996).
Sikora and Francis (2000) found lime and fly ash materials produced a hardened, nearly impervious surface layer capable of supporting equipment normally used at a windrow composting facility. They also found constructing a 0.73 ha (1.80 ac) windrow composting pad from lime and fly ash materials was approximately 28 percent of the cost
of a comparable-size 15 cm (6 in)-thick concrete pad. Another potential benefit of fly ash and lime composting pad materials is the P-sorbing properties reported by many researchers (Dou et al., 2003; Boruvka and Rechcigal, 2003; Lau et al., 2001; Brauer et al., 2005; DeLaune et al., 2006; Penn and Bryant, 2006). Dou et al. (2003) found fly ash reduced soluble P by 60 percent from converting H2O-P in dairy manure to NaHCO3-P, a
fraction less vulnerable to runoff losses. Significant quantities of Al2O3 and CaO also
were found in fly ash samples (Pathan et al., 2003), of which either compound can react with PO4-P. For this dissertation study, approximately 390 m3 (13,773 ft3) of fly ash was
provided free of charge by a local electric utility power generating station for composting pad construction.
This manuscript focuses primarily on documenting the effects of windrow composting and VFS buffers on runoff quantity and quality. However, windrow composting and VFS buffer effects can vary with the complex soil-water environment and different field conditions. These conditions include structure and species of VFS buffer vegetation, compost material, soil type, soil texture, fly ash composting pad material, type of contaminant, slope of the runoff area, and activities on the runoff area. The primary objective of this study was to quantify the effects of windrow composting practices and VFS buffers on losses of runoff (RO), runoff percent of rainfall (RO%), total solids (TS), nitrate-nitrogen (NO3-N), ortho-phosphorus (PO4-P), and total-
phosphorus (TP) during natural rainfall events. Critical consideration also was directed towards potential fly ash composting pad effects on runoff.
Materials and Methods
The study site was located at the Iowa State University Dairy Teaching Farm near Ames, central Iowa, USA (42° 00.564' N, 93° 39.267' W). The study site total area was 0.25 ha (0.62 ac) and was comprised of nine plots, each 6 m x 46 m (20 ft x 150 ft). The VFS buffer research plot area was selected on uneven terrain with an average slope of 5 percent. Dominant vegetation included 75 percent smooth brome (Bromus inermis Leyss.) and 25 percent switchgrass (Panicum virgatum L.) with a trace of mixed broadleaf species. Smooth brome occupied approximately 75 percent of each 1:1 VFS
buffer plot, primarily in the upslopes, and approximately 100 percent of each 1:0.5 VFS buffer plot in the upslopes. Switchgrass in the downslope areas occupied approximately 25 percent of each 1:1 VFS buffer plot, but only a trace was observed in the 1:0.5 VFS buffer plots. The average tiller population for VFS buffers was estimated at 2.7M tillers/ha. Tiller population was determined using a method from Arora et al. (2003). The tiller density value from this dissertation study contrasts with 9M tillers/ha (Arora et al., 2003) and 50M tillers/ha (Brueland, et al., 2003) from two other central Iowa VFS buffer research sites with similar vegetation types.
The major soil association at the research site is the Clarion-Webster-Nicollet association, with the minor soil association of Hayden-Lester-Storden in the area. All soils were formed in glacial till and local alluvium from till, with Clarion loam (a fine- loamy, mixed, mesic Typic Hapludolls) the dominant soil at the research site (Dewitt, 1984). The upslope composting pad surface area of the site was comprised of fly ash, a by-product of combustion from coal-fired power plants provided by Alliant Energy, Inc., Madison, Wisconsin, USA. The 0.13 ha (0.32 ac) composting pad area was constructed by machine grading to approximately a 2 percent slope, and fly ash was hydro-compacted to a depth of 30.48 cm (12 in).
This study focused on the effects of windrow composting practices and VFS buffers on runoff volume, sediment, and nutrient transport under natural rainfall conditions. Runoff data were collected from six events during 2002-2004. The composting period was based on 60-day durations during a particular research season, occurring approximately during the June-July early season (ES) and August-September late season (LS) time periods. The 2002 project year included one LS composting period, 2003 included one ES composting period, and 2004 included both ES and LS composting periods. Compost windrows were turned with tractor-assisted elevating-face conveyor and rotary drum flail type compost turning implements on a weekly basis for the first two weeks and bi-weekly for the remainder of the 60-day composting period. Compost samples also were randomly collected on a periodic basis for evaluating dairy manure compost characteristics (nutrients, moisture, and air-filled porosity), conducting nutrient mass balance analysis, and comparing these data to runoff quantity and quality.
Runoff data were analyzed for RO (mm), RO% (percent), TS (g), NO3-N (mg/L),
PO4-P (mg), and TP (mg) losses from natural rainfall events. Runoff treatments were
comprised of three compost windrow:VFS buffer area ratios that included 1:1, 1:0.5, and 1:0 (no buffer) control. The 1:1 and 1:0.5 area ratios represented a 6 m x 23 m (20 ft x 75 ft) fly ash compost pad area compared to equal and one-half size VFS buffer areas, respectively. All treatments had three replications for a total of nine runoff plots distributed in a randomized complete block design. Both compost windrow and VFS buffer plots used water-filled vinyl firehoses and 38 cm (15 in)-wide sheet metal borders, respectively, to minimize cross-contamination from adjacent plots. The firehoses, which could be drained quickly, were used in place of conventional sandbags to expedite the removal/replacement process for compost sampling and turning operations.
A tipping-bucket flow meter system (Hansen and Goyal, 2001) was used to measure and collect runoff from each plot after a rainfall event. A perforated four-inch diameter polyvinyl chloride (PVC) pipe collector was used at the downslope end of each VFS buffer area to direct runoff to the tipping-bucket system through 6 m-30 m (20 ft-98 ft)-long PVC flow pipes. The runoff samples were collected in 19-L (5-gal) plastic tanks through a plastic tube connected to an orifice in the 90° elbow at the end of the flow pipe for each runoff unit. Data loggers (Onset Computers Inc., Massachusetts, USA) connected to magnetic switches were used to measure tips for the tipping-bucket units. Runoff samples were collected after rainfall events of approximately 25 mm (1 in) or greater, and refrigerated until analysis at the Department of Agricultural and Biosystems Engineering Water Quality Laboratory, National Swine Research and Information Center, Iowa State University, Ames, Iowa, USA.
RO volume was determined from the tipping-bucket units and converted to equivalent depth in mm across each VFS buffer runoff plot. TS concentrations (g/kg) in runoff were measured using a gravimetric oven-drying method (Standard Methods, 1998). NO3-N concentrations (mg/L) were analyzed by the automated flow injection
cadmium reduction method using a Lachat Quickchem 2000 Automated Ion Analyzer system (Standard Methods, 1998). PO4-P concentrations (mg/L) were analyzed by the
Automated Ion Analyzer system. TP concentrations (mg/L) also were determined from filtered runoff samples using the ascorbic acid method (Hach Company, 2002). All TS and nutrient (NO3-N, PO4-P, and TP) concentrations were converted to total losses units
of g and mg, respectively. The significance among treatments was determined by using SAS software (SAS Institute, 2004). The GLM Procedure and LSMEANS Test were used to analyze differences among the VFS buffer treatment means at the 95 percent probability level.
Results and Discussion
Runoff Analysis and VFS Buffer Performance
There were a total of six rainfall events during 2002-2004 early season (ES) and late season (LS) composting periods that were used for analysis in this study. Runoff data were analyzed for RO, RO%, TS, NO3-N, PO4-P, and TP losses from natural rainfall
events. This included event dates, event numbers (E1-E6), and rainfall depths for composting periods 2002-LS (8-5-02E1/35 mm [1.4 in]); 2003-ES (6-25-03E2/81 mm [3.2 in], 7-5-03E3/61 mm [2.4 in]); 2004-ES (7-3-04E4/46 mm [1.8 in]); 2004-LS (8-26- 04E5/33 mm [1.3 in], 9-6-04E6/46 mm [1.8 in]). This manuscript discusses average total losses data values of the individual events for each ES and LS composting period during the three project years: 2002-LS (total event rainfall = 35 mm [1.4 in]), 2003-ES (total event rainfall = 142 mm [5.6 in]), and 2004-ES (total event rainfall = 46 mm [1.8 in]), 2004-LS (total event rainfall = 79 mm [3.1 in]).
Runoff analysis results in Figures 1-6 show significantly higher losses (p < 0.05) of RO, RO%, TS, NO3-N, PO4-P, and TP, respectively, from the 1:0 (no buffer) control
treatments for all composting periods. The 1:1 VFS buffers reduced levels of RO, RO%, TS, NO3-N, PO4-P, and TP by 98, 98, 98, 98, 97, and 96 percent, respectively. The 1:0.5
VFS buffers reduced levels by 93, 93, 94, 94, 93, and 90 percent, respectively. The overall average surface runoff loss reductions were 98 and 93 percent for the 1:1 and 1:0.5 VFS buffers, respectively, compared to the 1:0 control plots. Figures 1-6 also show the 1:1 and 1:0.5 VFS buffer treatments were not significantly different (p < 0.05). The
1:1 and 1:0.5 VFS buffer plots were 23m and 12 m (75 ft and 37.5 ft) in length, respectively. These VFS buffer performance results are similar to findings from other researchers. Edwards et al. (1997) and Lim et al. (1998) found concentrations of several surface runoff contaminants were significantly reduced in approximately 6 m (20 ft)-long VFS buffers, which ranged in lengths from 0-12 m (0-39 ft) and 0-18.3 m (0-60 ft), respectively. Arora et al. (2003) also determined a 30:1 (drainage area:VFS buffer area ratio) VFS buffer area could perform as well as a larger 15:1 VFS buffer area in significantly reducing agricultural herbicides in runoff, requiring less land removed from production to achieve desired results.
Figures 1, 2, and 3 show average RO, RO%, and TS losses, respectively, in surface runoff from the windrow composting/VFS buffer site. These results indicate the 2002-LS and 2003-ES 1:0 control treatments are significantly higher (p < 0.05) than the 2002-LS and 2003-ES 1:1 and 1:0.5 VFS buffer treatments. Figures 1-3 also indicate the 2002-LS and 2003-ES 1:0 control treatments are significantly higher (p < 0.05) than all VFS buffer treatments in the 2004-ES and 2004-LS composting periods. Since antecedent moisture conditions were minimal for the 2002-LS composting period (< 12 mm [0.5 in] rainfall 25 days before the 35 mm [1.4 in] rainfall event 8-5-02E1), the higher volume of runoff compared to the 2004 composting periods may be attributed to the more impervious surface condition of the fly ash shortly after composting pad construction in 2002. Although composting pad infiltration in 2003 also may have been structurally limited compared to 2004, the higher total rainfall and antecedent moisture conditions for 2003 (142 mm [5.6 in] combined rainfall total with > 50 mm [2 in] within seven days of rainfall event 7-5-03E3) probably elevated the 1:0 control plot runoff levels. For the 2004 composting periods, the significantly reduced runoff levels in the 1:1, 1:0.5, and 1:0 treatments may be due to freeze/thaw action that results in preferential flow cracks in fly ash and soil materials.
Other action that may have affected the fly ash composting surface during 2002- 2004 came from various mechanized implements used for manure and compost transporting, turning, and sampling operations. This grinding and scraping action resulted in surface compaction and deformation, accelerating the observed accumulation
of fly ash granules at the downslope end of the compost pad throughout the three-year project period. Although composting pad surface compaction during the composting periods may have caused a reduction in runoff infiltration, the accumulation of fly ash granules downslope may have resulted in increased runoff absorption. Punjab Agriculture University researchers reported the application of fly ash as a soil amendment was found to increase the available water content of loamy sand soil by 120 percent and of sandy soil by 67 percent (PAU, 1993).
Figure 4 shows average NO3-N total losses in runoff for 1:1, 1:0.5 VFS buffer,
and 1:0 (no buffer) control treatments. The 2003-ES 1:0 control plot NO3-N losses were
significantly higher (p < 0.05) than all other treatments and composting periods. These NO3-N losses roughly correspond to the event rainfall totals for each composting period,
but also may be attributed to the variable nature of NO3-N in runoff reported by other
researchers. Seymour and Bourdon (2003) found NO3-N concentrations varied by orders
of magnitude in dairy manure windrow compost leachate, with lesser NO3-N
concentrations and variability in runoff. They determined the variability to be a function of compost material age, compost process maturity, type of compost manure, and rainfall intensity and duration. This dissertation study used dairy manure for compost windrows in 2002 and 2003, and, due to availability, a mixture of horse, sheep, and beef manure was used for both ES and LS composting periods in 2004.
Figures 5 and 6 represent PO4-P and TP runoff losses, respectively, for the 1:1,
1:0.5 VFS buffer, and 1:0 (no buffer) control treatments. These results show significantly higher losses (p < 0.05) for the 1:0 control plots compared to the 1:1 and 1:0.5 VFS buffer treatments. These results also indicate significantly lower (p < 0.05) losses in the 1:0 control plots for 2004 ES and LS composting periods compared to 2002 and 2003. Figures 7 and 8 show PO4-P and TP runoff concentrations, respectively, for the 1:1, 1:0.5
VFS buffer, and 1:0 (no buffer) control treatments. These results are relatively lower than some other research findings. Seymour and Bourdon (2003) reported that P concentrations varied less than N species, but P tended to have higher concentrations in leachate compared to runoff. They found average PO4-P concentrations for leachate and
this dissertation study for all composting periods for the 1:1, 1:0.5 VFS buffers, and 1:0 (no buffer) control (Figure 7) were 5 mg/L, 6 mg/L, and 3 mg/L, respectively.
Figure 7 also shows the 2004-LS composting period PO4-P average concentration
for the 1:0 control plots were significantly lower (p < 0.05) than the 1:1 and 1:0.5 VFS buffer average concentrations. Given the potential fly ash P-reduction effect remains equal for all runoff treatments, this may suggest the VFS buffer vegetation could be contributing PO4-P to runoff. Haan et al. (2007) reported that grazing (vegetation
removal) stimulates new shoot and root growth, and non-grazed pastures (similar to VFS buffers) can gradually lose their capacity to sequester sediment and nutrients. Steinke et al. (2007) also found TP losses were similar for both prairie and turfgrass VFS buffer species in a study assessing runoff quality and quantity. They also suggested the natural nutrient biogeochemical cycling can result in nutrient loss to surface waters regardless of